Hormones control a vast array of bodily functions, including sexual reproduction and sexual development, whole-body metabolism, blood glucose levels, plasma Ca \(^{2+}\) concentration, and growth. Hormones are produced in, and released from, diverse places, including the hypothalamus and pituitary , the adrenal gland, the thyroid gland , the testes and ovaries , and the pancreas , and they act on target cells that are often at a considerable physical distance from the site of production. Since they are carried in the bloodstream, hormones are capable of a diffuse whole-body effect, as well as a localized effect, depending on the distance between the production site and the site of action. In many ways the endocrine system is similar to the nervous system, in that it is an intercellular signaling system in which cells communicate via cellular secretions. Hormones are, in a sense, neurotransmittersNeurotransmittersimilarity to hormones that are capable of acting on target cells throughout the body, or conversely, neurotransmitters can be thought of as hormones with a localized action.